This invention relates to a single tapered bushing for receiving and mounting a shaft within a rotatable hub so as to permit the shaft to be readily rotatably coupled to the hub and so as to accommodate variations in both concentricity and/or alignment between the shaft axis and the hub axis.
While such a shaft coupling and mounting system, as above-described, may have broad applications, one specific application is to permit a speed reducer, such as a shaft mount speed reducer, to receive a driven or output shaft and to accommodate variations in concentricity and alignment (within a limited range) between the output hub of the speed reducer and the driven shaft of an application to be driven by the speed reducer. Typically, a speed reducer has an input or high speed pinion shaft driven at relatively high rotational speeds by an electric motor or by another prime mover. The speed reducer has a housing which journals the input shaft and which houses and journals a speed-reducing gear train therein. The housing further typically has an output quill which includes a hub, with the quill hub being journaled with respect to the speed-reducing housing, and being driven at reduced speed by the gear train with a consequent increase in torque. The hub typically receives a driven shaft from a particular application so that the application is driven by the output hub of the speed reducer at a predetermined lower speed. Of course, it is important that the driven shaft and the speed reducer hub be substantially in axial alignment and be generally concentric with one another such that the shaft can be readily received within the hub, can be readily coupled to the hub, and such that undue bending moments and reaction forces are not applied to the output hub and to the bearings of the speed reducer, or to the application driven shaft or to its bearings, inasmuch as these moments and forces may result in a reduction in the operating efficiency and service life of both the speed reducer and the application. Also, it is desirable that the shaft be readily capable of both being coupled to and removed from the speed reducer, as required.
In the past, it has been known that sheaves or pulleys can readily be coupled to a respective shaft by means of a tapered, split bushing. However, the length of the shaft received in the sheave hub was relatively short. Examples of such sheave or pulley coupling bushings are shown in U.S. Pat. Nos. 2,331,498, 2,669,471, 3,368,833, 3,677,583, and 4,338,036, and in Australian Pat. No. 121,613.
Even more particularly, the problem of receiving and coupling an application shaft to the output hub or quill of a speed reducer in such manner as to accommodate variations in concentricity and axial alignment of the hub and the output shaft have been addressed in such U.S. Pat. Nos. 2,811,861, 3,590,652, and 4,452,547. However, these prior patents required the use of two tapered bushings and means for drawing the bushings into engagement with the shaft and the quill hub on both sides of the hub, so as to accommodate the longer length of the shaft received in the hub. This necessity of dual tapered bushings resulted in extra parts, material, labor, and cost required to receive and couple the shaft. Also, it required that both sides of the bushing be tightened or loosened for respective coupling and uncoupling of the shaft relative to the hub. These dual tapered bushings required the use of a somewhat longer shaft than was required for the length of the hub receiving them. Also, in removing these dual tapered bushings from the shaft, until one of the bushings was freed from the shaft, the oppositely facing bushings would tend to fight one another during removal because the shaft may become "frozen" to the bushings such that a loosening force on one acts as a tightening force on the other bushing. In an effort to overcome "freezing" of the shaft to the sleeve, a variety of coatings, such as various fluorocarbon resins including polytehafloroethylene (PTFE) and molybdenumdisulfide lubricants, have been used without apparent success. Often times, "wheel puller" tools were required to break the frozen shaft free of the sleeve. Not only was the use of such "wheel puller" tools time consuming, but often times additional lengths of the application shaft were required solely to permit installation of the removal tool on the application side of the hub. Removal of the hub is not an incidental problem because service is periodically required for the bearings of the speed reducer and the application. Also, in installing such dual tapered bushing mounts, the sleeves at both ends of the shaft must be tightened in general unison and uniformly torqued to predetermined torque levels.
In an effort to overcome these above-noted problems with the prior art double tapered bushings, single tapered bushings have been used within shaft mount speed reducers. However, this single tapered shaft extended only about halfway into the quill hub such that only a portion of the driven shaft received within the quill hub was engaged and gripped by the single tapered bushing. Also, this single tapered bushing was provided with external threads at its outer ends which were threadably received within internal threads provided in one end of a quill hub ring. The provision of such threads were expensive and were not entirely satisfactory in facilitating removal of the tapered bushing, particularly when the latter became frozen in the hub or on the application shaft.
Reference may be made to other U.S. Pat. Nos., such as 3,257,070, 3,398,597, and 3,442,559, for other references which may be in the same general field as the present invention.
While all of the above-identified prior references work well for their intended purposes, there has been a long-standing need of an effective method of securing and detaching a shaft to a speed reducer which minimized the number of parts, which accommodated a relatively wide range of misalignment between the shaft and the hub, and which was easier and faster to install and remove than the prior art shaft mounting systems.